Floating and submersible closed-contained aquaculture farming, and method of rearing fish

ABSTRACT

A fish rearing tank comprising the features of: a) an egg-shaped shell (1) with a generally vertical long axis and gradually narrowing shape towards its tip volume portion; b) said shell (1) forming a generally rigid tank; c) said shell (1) being closed; d) said shell (1) having one or more water inlets (11); e) said shell (1) having one or more water outlets (16, 29); said egg-shaped tank (1) for holding a water volume in its major lower volume portion and enclosing air in its minor, upper tip volume portion (4). Further disclosed is a method of rearing fish providing such an egg-shaped shell (1) and conducting bottom to top or ?reverse?-circulation of water through said egg-shaped shell (1) while maintaining its air-filled volume in said tip (4).

1. FIELD OF THE INVENTION

The invention relates to a closed-contained floating, and submersiblesystem for farming and storage of finfish and other aqueous species.

2. BACKGROUND OF INVENTION AND RELATED ART

During the last three decades, captured fisheries production increasedfrom 69 to 93 million tonnes; world aquaculture production increasedfrom 5 to 63 million tonnes. Although 70% of the Earth's surface iscovered by water, fish (including shellfish) only represent 6.5% of allprotein for human consumption whereas aquaculture represents around 2%.Fish is usually low in saturated fats, carbohydrates and cholesterolsand provides not only high value proteins but also a wide range ofessential micronutrients, including various vitamins, minerals, andpoly-unsaturated omega-3 fatty acids. Thus, even in small quantities,provision of fish can be effective in addressing food and nutritionalsecurity among the poor and vulnerable populations around the globe [1].

Current industrial aquaculture farming system is based on open net penculture. Examples given are typically for the Norwegian salmon industry.The description may just as well apply for salmon farming in othercountries, but is to a variable degree relevant to other aquacultureindustries. Oxygen is provided through incoming water and fish faecesand carbon dioxide (CO₂) and ammonium (NH₄) is discharged and carriedaway by the outflowing water.

The net pen production system leaves the fish population exposed to theopen environment. Water that flows through the net pen may carry harmfulmicroorganisms that potentially can infect the fish population. Severalnaturally occurring microorganisms² (Vibrio anguillarum, Vibriosalmonicidae, Aeromonas salmonicidae, Moritella viscosa, InfectiousPancreatic Necrosis Virus, Salmonid Alphavirus, Infectious SalmonAnaemia Virus, Piscirickettsia salmonis, Infectious HematopoieticNecrosis Virus, and many more) can cause disease in farmed salmonids[2]. The fish health status is subject to comprehensive surveillanceboth internationally (www.oie.int), from National animal healthinstitutes [3] and also by the farming companies. To combat the mostprevalent bacterial and viral diseases, pharmaceutical industry haveresearched and developed vaccines that are common in use. The value ofvaccination is undisputed in industry. Harmful microorganisms cannot beeliminated by vaccination, but vaccination immunises the fish andenables it to reject the infection and not develop clinical disease. Farfrom all harmful organisms can be prevented by vaccination.

Parasites prevalent to wild salmonids such as the sea louse(Lepeophtheirus and Caligus), infect farmed salmonids. The mostprevalent and widespread is the Salmon louse (Lepeophtheirus salmonis).Once clinical disease is established in one farm, the harmfulmicroorganisms represent an increased risk of contracting disease alsoto neighbouring farms [4].

As the number of fish farms are increasing, the high volume of farmedfish may become disproportional to the corresponding number of naturalhosts in a given area. At a certain production level, which may varyfrom place to place, multiple open net pen farming system run the riskof creating an ecological imbalance in which case a fish farm may becomeartificial incubators for harmful microorganisms and parasites [5]. Oncea fish population is harbouring harmful microorganisms or parasites, itbegins shedding to the surrounding environment and neighbour farms. Theshedding may expose and affect the net pens adjacent to the diseasedfish population, neighbouring sites and potentially also wild salmonidsresiding in habitats nearby the site. Understanding the exactinteraction is challenging and has over many years been subject tosubstantial scientific research [6].

The Salmon louse is common to farmed salmon. Its reproduction cycleincludes both free-living stages and fixed stages in which it resides onthe salmon skin. The reproductive capacity increases proportionally toincreasing temperature [7] and densities of farms [8]. The Salmon louseis phototactic (migrating towards daylight) and its infective stagebehaviour adapts to find a salmonid host predominantly residing in thetop layer of the marine environment. It has been suggested that theinfective stage of the Salmon louse remains in the first four meters ofthe surface [9, 10, 11]. Both research and practical farming confirmthat infestation levels are significantly less when farmed salmon aresheltered from the top 10 metres exposure of infective salmon louselarvae [9, 10, 11, 12, 13, 14]. However, the use of skirts around salmoncages to reduce infestation of salmon lice, result in reduced oxygenlevels and thereby it can stress the fish, impair welfare and feedutilisation [15].

When the salmon louse larvae infects a new host, it lives out of eatingmucus, skin tissue and blood off the salmon. The salmon louse may pickup microorganisms and carry for a period of time [16, 18]. Wildlife hasmany examples of parasites that serve as biological vectors. It is shownthat the salmon louse can be a biological vector for microsporidium[17]. Hence, the salmon louse may serve as a mechanical and biologicalvector that can carry harmful micro-organisms from fish to fish, fromone cage to another as well as from fish farm to fish farm.

Salmon louse from salmon farms may affect and harm wild salmonids onceshed in high numbers from salmon farms. Especially when the youngsalmonids are migrating from rivers to the ocean and pass nearby densefarming areas, the risk of negative impact is increasing. Likewise, seatrout populations do have their summer habitat in fjord and coastalareas where they may be exposed to Salmon lice during spring, summer andfall [19, 20, 21]. The spread of sealice, both magnitude, dynamics andpattern is crucial to understand how the challenge can be mitigated, andit is subject to intense research [22].

To protect the welfare of the farmed salmon and the wild salmonids,Government has enacted legislation to keep the level of sealice low insalmon farms, especially during the spring migration period. Since 1988salmon lice has been treated by use of chemical drugs likeorganophosphates, pyretroids, emamectin, teflu, -diflubenzuron,hydrogenperoksid as well as combination of these. Since the very startof combating the Salmon louse with chemicals, it has shown a remarkableability to develop resistance against any drug available. Since 2007,the salmon farmers along the Norwegian Coast have experienced thattreatments against the salmon louse have become less effective. Over thelast 7 years situation has impaired are currently seeingmulti-resistance i.e. no drugs are effective any more. In parallel, useof non-medical tools against the Salmon louse has accelerated. Forinstance use of cleaner fish have increased substantially [23]. Cleanerfish is fish that eats the Salmon louse off the skin of farmed salmon.This habit is observed also in nature and an elegant way of delousingfarmed salmon in a pen. Wrasse was introduced as cleaner fish thenineties. The fish were caught by locally and delivered to fish farms.Industry started to research farming of wrasse in 2009. In 2011, use oflumpfish was introduced as cleaner fish and has become popular due toits higher activity at lower temperatures. Lastly, a wide range ofphysical and mechanical methods have been tested to alleviate thedependency of drug use. Some of these demonstrate promising results. Theadvantage of using non-medical tools against the Salmon louse is thatthese do not generate resistance.

Still, in 2015, the salmon lice represent the biggest fish welfare andenvironmental challenge for the industry and has far reaching economicalconsequences [19, 24]. The combating of the salmon lice continue to bepredominantly handled by chemical methods and the use of drugs areincreasing. Supplemental to this, one is aiming to scale up use ofcleaner fish as well as other non-pharma tools.

Since 2009 the cost of combating sealice has risen from NOK 0.50/kg toNOK 5.00/kg and above. The problem of salmon lice is now so serious thatthe Norwegian Government has decided to restrict industry growth inareas where the salmon lice problem remains unresolved. Future growthwill be based on strict performance regarding sealice levels [25, 26].

In traditional net-pen farming of Atlantic salmon, after all fish areharvested, the site has to be fallowed for 2 months before new fish areallowed to be put in. The fallowing period occurs every second yearcorresponding to the production period of 14-22 months in the sea. Thefallowing regime is a sound practice adopted from agriculture andenables the site to cleanse and the seabed surrounding the farm torestore its original state after the farming production period with highorganic load due to feed spill and faeces from the fish [27].

In some areas subject to severe sealice burden, a mandatory zonefallowing of 1 month for all sites applies every second year as part ofthe two months fallowing of individual sites [28]. In fact, due tounder-performing sealice management, some sites have been enforced byregulation to reduce the production [29].

While having fixed assets like for instance a barge and numerous largecages sitting empty in a non-productive site, the fallowing periodstruly represent an extra cost.

Open net pen farming has during the last decades relocated to moreexposed sites with better water current conditions, which allows oxygenrich water to pass through. Consequently, the farmer can hold more fishper site. A well-located site can offer higher volumes of water passingthrough per unit of time compared to previous sites. But the increasedtotal flux of water may also cause problems. Assuming a randomdistribution of potential harmful microorganisms in the sea, the totalexposure will correspond to the volume of water flowing through a fishsite population. So does also the shedding [8]. Even in sites withimproved natural conditions, one may suffer disease and parasiticinfections. Although natural farming conditions have been much improvedby the relocation of sites, the mortality during one production cyclehas not improved correspondingly, and is averaging between 10-20% percycle across the Norwegian salmon farming industry. A recent studycarried out by Norwegian Food Safety Authorities following 307 millionfish from entry to harvest, concluded average mortality was 16.3% forAtlantic salmon and 18.3% for Rainbow trout [30]. Mortality in fishfarms may have numerous causes, for instance infectious diseases,production diseases, loss when handling and fish stress. The study aboveconcluded that issues related to osmoregulation at transfer andinfectious diseases constituted the major causes of mortality.

The open net pen systems show rapid variations in temperature, salinity,current, presence of algae, and occurrence of predators (wildlife thatsee farmed fish as prey). As many fish are unable to adjust to thevarious stress factors, welfare of the farmed fish is under pressure andelevated mortality is the result. Fish subject to stress, become moresusceptible to infectious diseases.

Farmed fish are fed extruded and pelleted feed. These are condensed andhigh-energy particles ranging from 3-12 mm in diameter. The feed isoffered to the fish in the cage largely by automatic feeders and minorvolumes by hand feeding. Cameras are located in many of the pens tomonitor and prevent over-feeding.

Adequate feeding in various weather conditions is challenging. It isrecognised that between 5-10% of the feed is never eaten by the fish andis discharged into the seabed surrounding the site [31]. The economicfeed conversion rate in salmon farms ranges from 1.0-1.4 with an averageof 1.15 in statistical review. The undigested part of the feed represent25% of the weight. Assuming one could capture both feed spill andfaeces, this would account for at least 30% of the nutrients of the feed[32]. Cost of feed is the single highest cost and represents between50-60% of the cost per kilo of farmed salmon. In other farmed species itis similar. There is a significant potential for cost saving and forsaving of resources and environment by eliminating the waste.

Fish also produce faeces that is discharged in the environment. Itcurrently represents organic waste. The faeces is rich in phosphorus,which is a scarce resource and in global demand. The fish waste can alsobe utilized for biogas production and blended with other types oforganic offal to become valuable fertilizer. The amount of dry matterfrom faeces in hatcheries varies a lot depending on the physical qualityof the feed, raw materials and size of fish [33]. While discharge issubject to filtering in land-based farming like hatcheries, all of thefaeces in sea farms are currently discharged into the water and carriedaway by the current. Depending on the tide and/or the current, there islittle or much spread of the faeces. Scientific studies suggest thatdischarging of faeces is presently not a limiting factor for theindustry as long as it sub-cedes the carrying capacity of the recipient.However, it is a waste of resources which could be better utilized.

Fish escape in the salmon farming industry is recognised as asignificant problem. Much resources are spent to prevent escape from thefarms and yet the endeavours are only rewarded with partial success. Dueto the significant number of farms in operation along the NorwegianCoast (˜600) representing maybe as much as 600 million fish, one shouldexpect more fish to escape. The fish farms are vulnerable to theelements. Escape prevention is high on the legislative and industryagenda. It has led to new technical regulations (NYTEK), and it issubject to close monitoring and investigation of incidents byDirectorate of Fisheries [34]. Semi-contained (open in the top) farmingunits have also suffered structural damage during storms.

Escaped fish may enter the rivers and interbreed with wild salmonstocks, destroy egg nests in the riverbed or potentially transferdisease. The magnitude of the damage to the wild stocks of Atlanticsalmon caused by escaped farmed salmon and rainbow trout, is stilldebated. However, it is undesirable to lose fish from a farm. Equally,it is undesirable that escapees end up in the vulnerable ecosystems insalmon rivers [21, 35, 36]. The unresolved escape issue represents arestriction on the Norwegian industry for further growth. Largesea-areas in the fjords that are ideal for farming, are closed due tothe risk of escape.

In conclusion, we can say that current net pen fish farming has asignificant and untapped potential for increased feed utilization,reduced environmental impact as well as improved fish welfare and wasterecycling management.

DESCRIPTION OF RELATED ART

The inventor is familiar with the prior art inventions listed below noneof which represent a similar invention as the one in this application.Parts of the system are described from other sectors and covered byprior art.

US 20060265940 A1 “Egg-shaped live bait well system” describes not afish tank, but a live bait well for storing and maintaining live bait.It includes a container having an egg shape with the tip pointingdownwardly. The bait container includes a top lid connected by a hingeto a main body and a water tight seal provided by a gasket. Thecontainer includes moulded cooling device holders and a drain. A waterpurification system is provided that includes a pump and an oxygenaerator infusion device and a charcoal filter in line in a tube systemconnected to an outlet port and an inlet port of the main body of thecontainer.

U.S. Pat. No. 4,798,168 A “Arrangement for farming of fish, shellfishand other marine beings” describes an vertical cylindrical arrangementwith a funnel-shaped bottom. It comprises a bag having circularcross-section submerged in water with an upper edge of the bag definingan opening at the water surface and fastened to floats or disposed in aland base arrangement. The cloth of the bag is watertight. A hose andpump arrangement is provided to suction water from a depth having afavourable water temperature, and expel the water within the bag via anoutlet at the water surface, the outlet being oriented tangential to thehorizontal cross-section of the bag.

U.S. Pat. No. 8,925,489 “Fish farming pen” to Jorn Hoie, describes afish tank for use in water and comprises a main part (1) made of awatertight, substantially rigid material and has an outlet for effluent(12). The main part (1) is hemispherical. It may slip unhindered throughthe water along a spherical path without affecting the body of waterinside the cage. The forces acting on the main part (1) from thesurrounding water act mainly along the shell, not perpendicular to theshell.

US 20060162667 “Aquatic habitat and ecological tank” describes aself-contained, floating fish aquaculture tank for containing fish andother aquatic animal, plant, and algal species. It includes a series ofpanels joined together by flexible connecting joints to form acylinder-shaped tank enclosure with a conical bottom surrounded at ornear the open end by a water-resistant and buoyant foam. The tank isplaced into a body of water where it floats and maintains the same watertemperature as the surrounding body of water. The tank includes a wastecone at the bottom of the tank enclosure to which the lower portion ofeach panel is attached.

U.S. Pat. No. 8,171,884 “Method and system for feeding aquatic animals”comprises a method and a system for feeding aquatic animals. The methodincludes submerging, at least partially, a chamber in a water reservoir,the chamber comprising a bladder comprising food for aquatic animals,periodically pumping water from the water reservoir into the chamber,exerting, by the pumping, a force on the bladder, and thereby dispensingthe food into the water reservoir.

U.S. Pat. No. 4,224,891 “Semi-submersible vessel having a sealed closedchamber of truncated ovoid shape” describes modules each comprising asealed chamber of annular cross-section, a partially immersed supportstructure secured to the chamber, and a platform or deck carried by thesupport structure. The support structure comprises a trusswork oftubular members. The sealed chamber comprises a plurality of toroidalstorage reservoirs and ballast tanks and has a truncated egg shape belowthe water surface and open in the wider, upper truncated end.

U.S. Pat. No. 3,204,605 “Live fish grading apparatus” describes alongitudinal passage with a longitudinal bars forming a grating forsorting small fish dropping through the grating, and bigger fish forpassing along on top of the grating.

U.S. Pat. No. 2,011,365 “Adjustable sieve describes such adjustablesieve” is an adjustment mechanism for a sieve.

U.S. Pat. No. 7,371,162 “Sieve adjustment mechanism for an agriculturalcombine” is an adjustment mechanism for a sieve. opening size of sievesegments of the cleaning system of an agricultural combine disposed inend to end relation, which allows jointly adjusting the sieve sizes, orseparate adjustment.

JP06276887 “Culture crawl” describes a submersible or semisubmersiblespherical shell with a soft hull kept in spherical shape and buoyancycontrolled by air pressure. The fish container has a lower outlet forfaeces in the bottom and a fresh water inlet in a top portion.

NO318527 describes an open top vertical cylindrical tank with anear-hemispherical tank bottom with a transition to a funnel-shapedlower end. A sludge separating outlet is arranged on a stand pipe in thebottom of the funnel.

U.S. Pat. No. 4,010,704 shows an antenna buoy with a three quarterspherical rigid shell arranged for not rolling in sea waves. An objectof the US patent is to provide a sphere tuned against roll and heaveproviding a stable platform for the drill rig.

U.S. Pat. No. 3,487,484 shows an anchored drilling platform comprising ahemispherical shell hull with a closed deck and a derrick holding adrill pipe string to the sea floor.

Passive grading by use of a net providing columns in-between which thesmall fish may pass, is well known in the industry.

3. FIGURE CAPTIONS

FIG. 1 shows a vertical cross-section and partial view of a first,surface version, a first embodiment of the fish tank of the inventioncomprising a vertically oriented, tip-up fish tank filled with water toa desired level and with an air-filled tip portion, and having a waterintake near the bottom end and a water outlet near the internal waterlevel. In an embodiment the surface embodiment has a ring-shapedfloating collar. In an embodiment there is arranged a sludge storagering with the floating collar, and a sludge separation system isarranged near the internal water surface perimeter.

FIG. 2 illustrates a vertical cross-section and partial view of asecond, submersible version, a second embodiment of the fish tank of theinvention comprising a vertically oriented, tip-up fish tank filled withwater to a desired level and with an air-filled tip portion, and havinga water intake near the bottom end and a water outlet near the internalwater level. In this submersible version the water circulation dischargemodule is still near under the internal water surface and the waterinlet to the tank is near the bottom of the tank, and preferably neartangential.

FIG. 3 illustrates the above submersible embodiment, now in a submergedstate. Air has been let out through the laterally and near top arrangedair valve and the internal water level has been allowed to rise to thislevel, from where it in this embodiment can not rise further. In anembodiment of the invention a mooring line is tightened in order tocontribute to the submerged stability. In an embodiment the buoyancyring and the ballast tank is arranged about the broadest portion of theegg-shaped tank. Still in this submerged state the water mayadvantageously be let in through the preferably tangential inlet nearthe bottom of the tank, and let out near under the internal surface eventhough this internal surface has been raised. In an embodiment thesludge is taken out via a level-adjustable passage on an internallyfloating device and led via a sludge drain to the external circularholding tank. Thus the entire egg-shaped fish tank may be operated forfish farming while being submerged, without any significantinterruption.

FIG. 4 is an illustration of an embodiment of the invention wherein theparticles have concentrated at the water surface towards the perimeterof the tank. By the higher level of the water inside the tank comparedto the outside of the tank i.e. the level of the sea, the surplus waterin the circular holding tank is drained. The particles in the fish tankfloat over a level-adjustable passage built like a floating device, andinto the circular holding tank from which collection is possible bymeans of sludge sucking device.

FIG. 5 comprises several drawings and they show details of thevertically movable grid and its operation.

In FIG. 5a The fish grid is shown in a folded-in state. In this state itmay be stored in the top of the tank while not operating down in thewater volume.

In FIG. 5b the fish grid is shown in a partly unfolded or expanded statefor use down in the water volume of the tank.

In FIG. 5c is illustrated a suspension for crossing ellipsoid bars. Thebars are turnable by stags (23 d) mounted perpendicularly to thedirection of the bars.

FIG. 5d the grid is shown in four different positions:

5 d 1: Folded and stored in top position

5 d 2: Folded and lowered in the bottom

5 d 3: Expanded in the middle

5 d 4: Catching and crowding fish

FIG. 6 illustrates after the water in the tank being evacuated byreversing the pumps while sealing off the water discharge area. The tankwill gradually be elevated in the water, and tilted to the side whilestill floating on the sea.

4. DESCRIPTION OF EMBODIMENTS OF THE INVENTION 4.1 SUMMARY OF THEINVENTION

The applicant has invented a closed-contained floating and submersiblefarming system for farming and storage of finfish and other aqueousspecies, where a container (hereinafter the “tank” or the “fishtank”)its geometrical shape, water flow system, anchoring system, fish faecescollection, the adjustable fish grid collector and separator(hereinafter “the fish grid”), and related operating functions,represent inventive solutions that in sum significantly reduceenvironmental impact, improved waste management and productionperformance, as well as enhancing fish welfare. Furthermore, theinvention expands the area where fish and other marine species can befarmed, including inshore and offshore, fresh water lakes, rivers andwaters covered by ice parts of the year. The invention is depending onreliable supply from on-shore electrical power supply.

The invention is a fish tank comprising the features of:

-   an egg-shaped shell (1) with a generally vertical long axis and    gradually narrowing shape towards its tip volume portion (4);-   said shell (1) forming a generally rigid tank;-   said shell (1) being closed,-   said shell (1) having one or more water inlets (11),-   said shell (2) having one or more water outlets (16, 29),-   said egg-shaped tank (1) for holding a water volume in its major    lower volume portion and enclosing air in its minor, upper tip    volume portion (4).

The invention is also a method for providing and using such a tank asdefined independently in the set of claims.

Dependent claims to these claims are listed in the attached set ofclaims.

4.2 DESCRIPTION OF THE DRAWINGS

The drawings show two different variations of the invention: FIG. 1shows the tank as a contained fish rearing system which is heldpermanently in surface position. Hereinafter this variation is referredto as version 1. FIGS. 2 and 3 show the tank in a surface and submergedposition respectively. Hereinafter this variation is referred to asversion 2.

4.3 DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION PERTAINING TOBOTH VERSION 1 AND VERSION 2

The invention comprises an egg-shaped container (1), hereinafter the“tank”, “unit” or the “fish-tank” (1), that provides a complete andseamless double-curved surface that is significantly stronger thancurrent systems. With its solid and firm construction and innovativecharacteristic described below under advantages and properties no. I,Ill, and VIII, the tank provides a significantly reduced risk of fishescaping. While in net pen farming, only the net is keeping the fishfrom escaping, this tank is fully contained with a solid barrierthroughout the sea phase of the production. The material used forconstruction may vary depending on the location and can be composite,rubber, fibre armed canvas, combination of these or other materials. Theinvention utilizes assembly and mounting techniques known from the shipbuilding industry.

The shape of the tank (1) with its centre tube (2), diverts forcescaused by wave actions, wind, current and tension from mooringarrangements (3) and the tank's geometrical structure sustains andreliefs its integrity while under deflection caused by external forces.The egg shape of the tank increases the volume in which fish can be heldand consequently the production accordingly compared to hemisphericstructures. 90% of the interior volume consists of water whereas 10% isair located in the top, hereafter also called the tip portion (4) of theegg-shaped shell (1), please see FIGS. 1, 2, and 3. The air cap in thetip (4) holds atmospheric pressure and communicates with the outside airby a ventilation fan that also regulates adequate air intake.

The egg shape of the tank with its gradually narrowing shape towards thetop provides a unique and surprising wave attenuation. The waves arebroken and delayed by the exterior collar. When internal waves arehitting the double-curved wall on the other side, the wave isattenuated. The vertical and horizontal curving produce a wave reflexthat calms the wave rather than returning it full force.

In hemispheric or cylindrical fish tanks, the wave hitting the tank fromoutside goes straight and unbroken through on the inner side and bouncesback from the wall. If the wavelength on the outside hits the wavelengthof the inside, resonance can occur. The amplitude of the inner wave canthen double and cause unpredictable waves, damage and potentially harmfish and people.

The centre tube provides a guide for equipment that is mounted insidethe tank (ex. the fish grid, working platform (6), sensor equipment forwater quality, and fish welfare monitoring, and channel for supplementalad optimised water flow into the centre part of the tank. The centretube water supply secures satisfactory replacement of water in thecentre part the tank and enables the operator to maintain goodcirculation throughout the entire water volume. Also, the tube defines aminimum track for the water near the centre of the tank. Thereby itprevents the water from entering the centre which would have created adownwards vortex causing counter-current and stagnant water.

In case of emergency, ex. toxic algae in intake level, the ability toclose, filtrate or treat the water intake can be built into the tank.Sensors that can provide the operator with early warning of an upcomingalgae or environmental threat are mounted beside the water intakes (9).

The water intakes can be extended to variable depths. If required, theycan be equipped with means to disinfect, filtrate or any other watertreatment method that reduces the risk of harmful microorganismsentering the tank.

In the bottom of the tank and integral to the construction, fixedballast is built in (7) for the stability of the tank.

The tank can be manufactured in any size. Typically, for Atlanticsalmon, the size would be 4500 m3 for fish up to 1 kilo. For fish up to5.5 kg typical size would be 22000 m3. The latter tank could hold 50kg/m3 and totally 1000 tonnes per tank. If water exchange is workingideally, the tank will be built as larger units as well.

The tank has its power supply from a central barge or land-base.

Two main pumps (8) with check-valves (9) and inlet strainer (10) aremounted below the bottom of the tank. The water-intake is at least 20meters below surface. The diameter of the intake pipe is in oneembodiment 2250 mm. The two water inlets (11) in the tank are positionedhorizontally and tangentially just above the fixed ballast. The pumpsprovide a circular flow of water to the top.

In addition, a pump is mounted in the centre tube (12) and pumps waterup the tube. The centre tube is sealed off near water level to rise thewater pressure inside the tube. Water can be let out through remoteoperated hatches at ¼^(th) up the tube (13), 2/4^(th) (14) up the tube,and ¾^(th) (15) up the tube. The three levels are each optional and canbe run one at the time or in combination. This function secures theoperator to control the waterflow in the tank.

The tank's geometrical shape resemble that of a bird's egg and providesan innovative possibility to concentrate and collect fish faeces andfeed spill. The particular composition and design of the structure withits gradually narrowing shape will increase the speed of the water flowand enhance vertical and centripetal forces on particles as the waterrises to the top of the tank.

The particles will concentrate at the water surface towards theperimeter of the tank (17). By the higher level of the water inside thetank compared to the outside of the tank i.e. the level of the sea, thesurplus water in the circular holding tank (19) is drained. Theparticles in the fish tank float over a level-adjustable passage (18)built like a floating device, and into the circular holding tank fromwhich collection is possible by means of sludge sucking device. (FIG.4).

In most locations, it is neither necessary to semi-submerse the tank,nor to fully submerse it. For such use, version 1 is suitable (FIG. 1).Version 1 has its buoyancy at the water level (20). The surface buoyancyprovides sufficient stability and control so that central verticalmooring is redundant.

Fish are given extruded and pelleted feed ranging from 3-12 mm indiameter. The feed access the tank through air driven pipes from acentral barge or land-base. It is loaded into two feeding pipes (21)mounted inside the centre tube. These reach 3 meters above water leveland end approximately 5 and 10 meters above the bottom of the tank atwhich point they exit the tube into the tank (22). At the top of thefeeding pipes, an air driven piston is mounted. After the filling withdesired volume of feed into the pipe, the piston moves downwards, thefeed is pushed out of the lower opening of the pipe providing fish withbatches of feed.

The fish grid (capturing and grading devise) (23) is stored in the topof the tank. The grid is shaped like a flexible, foldable and expandabledevice. See FIG. 5a (folded) and 5 b (expanded).

The grid is integral to the tank and consists of two main parts:

-   -   a. The central frame (23 a) equipped with hinges for foldable        wings (23 b) on the outside, and, on the inside, suspension for        crossing ellipsoid bars (FIG. 5c ). The bars are turnable by        stags (23 d) mounted perpendicularly to the direction of the        bars. When turning the central bar mechanically, all of the bars        will turn accordingly. While turned, the space between the bars        are gradually opened and enables the operator to decide which        size of fish that shall be permitted to pass between the bars        and which are kept above the grid. While turned fully to the one        side, the ellipsoid bars form a water permeable but dense        surface that will catch all fish. Bars in open (23 e) and closed        (23 f) position is shown in FIG. 5c . Depending on the species        of fish farmed, the hinging, shape and spacing of the ellipsoid        bars may vary.    -   b. The foldable and expandable wings that are hinged on the        central frame. When in its stored position, the grid is located        at the top of the tank. In this position, the wings are folded        inwards (FIG. 5a ). The grid can be lowered slowly into the tank        by use of a winch. The wings will stay folded until released        manually. Once lowered into the water the folded wings allow the        fish to pass outside so that desired volume of fish are above        the grid at the point when the wings are unfolded (FIG. 5b ).    -   From here, or at any depth in the tank, the wings can be        unfolded by the force from the winch. The outer edge of the        wings these are equipped with small guiding wheels (23 g) in        order to adjust to the variable radius of the tank. The wings        form a water permeable but dense surface that collect all fish.

In FIG. 5d the grid is shown in four different positions:

-   5 d 1: Folded and stored in top position-   5 d 2: Folded and lowered in the bottom-   5 d 3: Expanded in the middle-   5 d 4: Catching and crowding fish

Functionality of the Grid:

At the desired depth, wings are unfolded and divides the tank into twocompartments,—one above the grid and one below. Slowly but steady thegrid is elevated. The grid will serve the function of

-   -   i. collecting parts of the fish population    -   ii. collecting all fish in the tank    -   iii. grading off the fish ready for harvest    -   iv. counting of fish from one compartment to the other

The grading and collection grid is integral to the tank. Passive gradingby use of a net providing columns in-between which the small fish maypass, is well known in the industry. However, although it is developedexclusively to the unit, it is also adaptable to other circular-shapedor hemispheric tanks. It's mechanical construction and functionality areunique. Once elevated slowly through the fish population it can serve as

-   a) A grader for harvest size fish by leaving smaller fish to pass    between the bars that are crossing the central frame. Typically, an    opening between the bars of 15 cm will grade off all fish above 4    kg.-   b) A grader for medium sized fish at large and medium size at around    average weight of 1.5 -2 kg. Typically, a opening of 8 cm will grade    off fish that are above 1.5 kg.-   c) A fish collecting system to empty the tank by turning the bars to    a closed position.-   d) A fish collection system to count the fish in the tank by turning    the bars to closed position.

The tank is not transparent to daylight. It must have artificiallighting inside. Absence of daylight enables the operator to controldaylight hours including shortening the day and year cycle.

The tank can be cleaned outside and inside by use of automatic washingmachines. Washing of the tank can be done while in operation by use ofan automatic surface cleaning device. It can also be carried out afterall fish are harvested. The water in the tank is evacuated by reversingthe pumps while sealing off the water discharge area. Then, the tankwill gradually be elevated in the water, and tilted to the side (FIG.6).

Once almost emptied of water, all vital functions can be serviced onsite, it can be towed to nearest dock, or hauled on board a servicevessel for timely maintenance and repairs. The remaining water can bepumped out by use of a sink pump. The whole operation can be completedin one week only, at which time the tank is again ready for next groupof fish. The tank is then ready for returning to the same site or to anew site. By shortening the “out of operation” time with several weeks,the utilisation of fixed assets improves significantly.

4.4 DETAILED DESCRIPTION OF THE INVENTION PERTAINING SPECIFICALLY TOVERSION 1

The buoyancy in version 1 consists of a collar integral and outside thetank located at the surface. The collar has multiple buoyancy segmentsbuilt into the ring. If one segment is punctured, the remaining ones areable to retain sufficient buoyancy and the tank stable. Apart from thebuoyancy, the ring has the functionality of sludge storage (19),increased water ballast, mooring for boats and entering area, as well asfixing for horizontal mooring (3).

4.5 DETAILED DESCRIPTION OF THE INVENTION PERTAINING SPECIFICALLY TOVERSION 2

The enclosed geometrical shape allows the tank to become semi-submerged(so that it barely breaks the surface) shown in FIG. 2, or submergedbelow the surface shown in FIG. 3, while still retaining its operatingfunctions. The version 2 has its buoyancy (24) and ballast tank (25)located to the widest part of the tank.

Version 2 of the tank may therefore be operated in three main positions;above surface, semi-submerged, and submerged, or any other desiredposition in-between.

The central vertical line, mounted inside the central tube in a separatetube in centre, is connected to a water-driven hydraulic cylinder orwinch (28) at the top of the pipe, remains tight at all times.Horizontally, the tank may be moored into an existing mooring system ina farm, but may also be anchored satisfactory with the central verticalline only, or by other means. When the tank is moored to the seabed, itwill be regulated according to the tide. The hydraulic cylinder has anadjustable pressure release valve to secure stable tension of thecentral vertical line and thereby keeping the tank in the correctvertical position.

The anchoring system reduces the vertical movement when the tank isexposed to wave action. This is particularly important in heavy waveswhere a pronounced vertical movement puts extra strain on mooring lines.

The tank becomes submersible by filling of the water ballast tanks andby tightening the central vertical mooring line (26). I detail thefunctionality is as follows:

While in surface position, a remotely operated valve is located wellabove the water line (27). The part of the air cap at the top of thetank is evacuated by opening the valve while central vertical mooringline is tightened. At the point where only a slightly positive buoyancyis obtained, the top valve is closed. The remaining buoyancy isneutralised by tightening the vertical central mooring line. The forcerequired is provided by a water-driven hydraulic cylinder (28) or winchat the top of the tube. The hydraulic cylinder is remotely controlled.Once in the submerged position, the tank can be brought to the surfaceby reversing the order of action. When releasing the tension of thevertical central mooring line, and emptying the ballast tanks, the tankis forced to the surface by its increasing buoyancy.

In all the positions, be it partly or wholly submerged, the tank retainsits full functionality and farming capabilities.

Some of the air cap inside the tank (4) is retained to allow air accessfor the fish. Salmonids, common to fish farming, for instance Atlanticsalmon (Salmo salar), Rainbow trout (Onchorhynchus mykiss), and Cohosalmon (Oncorhynchus kisutch) have all physiological need for swimbladder pressure regulation. Air access is therefore important inversion 2. It is shown that Atlantic salmon may perform without air fora period of seven days while after this period it will gradually reducefeed uptake and thrive less [12].

The central vertical mooring line in combination with regulation of thebuoyancy allow the tank to stay in surface position for service, tobecome semi-submerged, or submerged so that it can withstand heavy waveswhile retaining its operational functions. In semi-submerged andsubmerged position, the tank deflects the wave forces. This offerssignificant benefits to the industry, as follows:

-   -   i. Possible to farm fish in semi-exposed sites    -   ii. Possible to farm fish in exposed sites    -   iii. Possible to farm fish in areas with ice during winter while        having access to temperate water below. The discharge of        temperate water will keep the tank from freezing in.    -   iv. Less lost feeding days due to poor weather in any site    -   v. In surface position a sheltered working position for the        operator that supports health and safety

The water discharge module (29) is still outside the tank in Version 2well below water surface. The innovative possibility to concentrate andcollect fish faeces and feed spill pertains also Version 2. However, thelevel-adjustable passage (30) for the drainage of concentrated fishfaeces is mounted on a floating device (31) inside the tank since thewater level may change. The sludge is drained (33) into the circularholding tank (32) which is located outside the fish tank, where surpluswater is drained off. The sludge-draining boat cannot enter before thetank again is in surface position (FIG. 2).

Because of the higher water level in the tank while in submergedposition, the feeding pipes (34) are extended well above the water lineinside the tank.

5. Properties and Advantages

5-I:

The invention provides the first seamless fully contained large-scalesurface and submersible fish rearing and storage system with capacity tobe fully operational in variable water depth position, wave -,temperature -, and climate conditions.

5-II:

The fish tank of the invention significantly reduces the cage to cage,and the site to site infection pressure by

-   a. Sheltering the farmed fish population from direct influence of    surface water that may contain harmful microorganisms from    neighbouring farms.-   b. Eliminating the risk of negative influence of marine preying    birds (ex. seagulls, terns, herons etc.) whom may carry harmful    microorganisms, by providing a fully contained fish tank.-   c. Avoiding the entry of Salmon lice larvae by having the water    intake below 20 meters and providing a fully contained cap, avoiding    any splashing of waves and surface water into the cage.-   d. Avoiding occurrence of salmon lice in farmed fish reared in the    tank, eliminate the shedding of salmon lice, and thereby eliminate    infection pressure to wild salmonids caused by current farming    practices.-   e. Protecting the fish from harmful microorganisms that are known to    be carried by Salmon lice as vector    5-III:

The fish tank of the invention provides a complete physical barrieragainst predators.

Farmed fish is prey for many wild animals like birds, otters, mink,seals, sharks etc. Predators are attracted to the farm by the smell, thesight and turning shoal of fish. Predators often cause damage to thenets. Predators can be vectors for microorganisms that can cause diseasein farmed fish as they migrate from cage to cage and site to site. Whiletrying to break into the cages, predators may harm or kill fish and tearthe nets in the cage systems. While observing the predator, the fish areseverely stressed and loose feed apetite. Stress can also elicit diseasedue to the suppression of the immune system. Exposure to predatorsreduces fish welfare.

5-IV:

The fish tank of the invention improves the feeding efficiencysignificantly compared to current farming practices. Current Norwegiansalmon farming practice has a feed spill (fed but non-eaten feed)averaging 7%. The conditions in which net pen farmed fish are fed,display a great variation due to current, waves, sight and time of theyear. Even though various types of control mechanisms are in place, likefor example cameras, sensors etc, large amount of feed are lost. Feedingin the fish tank takes place at two different depths, the pellets aredisseminated by the circular and upwards movement of the water, and fishcan be fed to satiation by meal feeding. Cameras in the top layer of thetank will disclose over-feeding securing that an accurate meal isdelivered to the fish. The tank provides a fully contained andcontrollable unit which significantly reduces feed spill.

5-V:

The fish tank of the invention has a new water flow system. All currentsemi-contained systems are pumping water through riser pipes. Waterenters at the surface of the prior art units and discharges at thebottom or in the walls near the bottom. Opposite to this, the flow inthe tank of the present invention is creating an upward circular currentand discharges through a unit near the top. This counter principle doesnot cost more energy since the head difference of the water inside thetank compared to the outside, is still similar to current semi-containedsystems. In addition, the central tube provides a guiding wall thatprevents a typical vortex and counter-spin in the centre of a tankwithout centre tube. Furthermore, the upwards water supply through thecentral tube secures sufficient water replacement and circulation in thecentre of the tank. The mixing of the various water supplies enables theoperator to adjust the flow optimal to the fish welfare. The system alsoprovides the operator with an improved overview of the tank sinceeverything (feed spill, faeces, dead fish etc) are brought upwards andend up concentrated at the surface.

5-VI:

The fish tank of the invention significantly reduces discharge of faecesparticles compared to current open net pen farming. The water flow(property 5 above) and the beneficial shape of the tank causes thefaeces to concentrate and to surface at the perimeter of the tank. Fromhere, it is possible to decant it into the collection and storagefacility (30, 31, 32, 33). The ring sludge storage can keep sludge for acertain number of days. At the end of the period, the sludge iscollected by a boat, which carry a sludge tank and a sludge-vacuumingdevice. Fish faeces is a valuable resource and particularly rich inphosphorus. Phosphorus as a mineral, is in world demand. The sludgecollection system of the invention is integral to the tank and it isoperational for both version 1 and 2. The sludge collection systemaccording to the invention significantly reduces organic discharge perkilo of fish produced and it enables the industry to retrieve a valuableresource.

5-VII:

The grading and collection grid of the fish tank of the invention isintegral to the tank. Once elevated slowly through the fish populationit can serve as

-   a) A grader for harvest size fish by leaving smaller fish to pass    between the bars that are crossing the central frame. Typically, an    opening between the bars of 15 cm will grade off all fish above 4    kg.-   b) A grader for medium sized fish at large and medium size at around    average weight of 1.5 -2 kg. Typically, a opening of 8 cm will grade    off fish that are above 1.5 kg.-   c) A fish collecting system to empty the tank by turning the bars to    a closed position.-   d) A fish collection system to count the fish in the tank by turning    the bars to closed position.    5-VIII:

The central vertical mooring line in combination with regulation of thebuoyancy allow the tank to stay in surface position for service, tobecome semi-submerged, or submerged so that it can withstand heavy waveswhile retaining its operational functions. In semi-submerged andsubmerged position, the tank deflects the wave forces. This offerssignificant benefits to the industry, as follows:

-   -   i. Possible to farm fish in semi-exposed sites    -   ii. Possible to farm fish in exposed sites    -   iii. Possible to farm fish in areas with ice during winter while        having access to temperate water below. The discharge of        temperate water will keep the tank from freezing in.    -   iv. Less lost feeding days due to poor weather in any site    -   v. In surface position a sheltered working position for the        operator that supports health and safety        5-X:

The tank of the invention offers a unique opportunity to control thedaylight during the entire sea phase. Although photoperiod treatment iscommon in fish farming, none of the treatments can offer permanentcontrol of daylight in sea over months. The tank provides permanentcontrol over light conditions and thereby control over the physiologicalfunctions in fish. Lights are mounted both above and below watersurface.

5-XI:

The tank of the invention offers improved productivity per productionsite since it can be cleaned and fallowed during one week only asopposed to traditional farming equipment.

5-XII:

With its solid and firm construction and innovative characteristicdescribed in 5-I, 5-III, and 5-VIII, the tank of the invention providesa significantly reduced risk of fish escaping. While in net pen farming,only the net is keeping the fish from escaping, this tank is fullycontained with a solid barrier throughout the sea phase of theproduction. The walls are robust and cannot be teared. The environmentalforces are easier deflected since the well-balanced geometrical shapeabsorbs the impacts in a more optimal way.

For version 1 the segmented buoyancy belt is located in the surface andwill enable the tank to take direct hit from the sea, boats and debris.

5-XIII:

The double-curved surface provides a wave attenuation effect both atfront-, and rear end and reduce the risk of wave resonance in the tank.

6. REFERENCES

-   -   1. Fish to 2030. World Bank report. 2013.    -   2. Kent M L and Poppe T T, Editors of text book. 1998. Diseases        of Seawater Net pen-reared Salmonid Fishes. Fisheries and Oceans        Canada. Nanaimo, BC.    -   3. Norwegian Veterinary Institute. Annual Fish Health Report.        http://www.vetinst.no/eng/Publications/Fish-Health-Report/Fish-Health-Report-2014    -   4. Jones S R M, Bruno D W, Madsen L, and Peeler E J. 2015.        Disease management mitigates risk of pathogen transmission from        maricultured salmonids. Aquaculture Environment Interactions.        Vol. 6: 119-134.    -   5. Hoech P A, and Mo T A. 2001. A model of salmon louse        production in Norway: Effects of increasing salmon production        and public management measures. Diseases of Aquatic Organisms,        45: 145-152.    -   6. Raynard R, Wahli T, Vatsos I, and Mortensen S. 2007. Review        of diseases interaction and pathogen exchange between farmed and        wild finfish and shellfish in Europe. The DIPNET project under        the 6^(th) EU Framework Programme Priority 8, Scientific Support        Policy (SSP). Published by Veso, Norway on behalf of the        Consortium.    -   7. Heuch P A, Nordhagen, J R, and Schram T A. 2000. Egg        production in the salmon louse [Lepeohtheirus salmonis (Kroyer)]        in relation to origin and water temperature. Aquaculture        Research, 31: 805-814.    -   8. Jansen P A, Kristoffersen A B, Viljugrein H, Jimenez D,        Aldrin M, Stien A. Sea lice as a density-dependent constraint to        salmonid farming. Proceedings of the Royal Society of London.        Series B: Biological Sciences. 2012;279:2314-2322.    -   9. Hoech P A, Parsons A, Boxaspen K. 1995. Diel vertical        migration: a possible host-finding mechanism in salmon louse        (Lepeophtheirus salmonis) copepodids? Can. J. Fish. Aquat. Sci.        52,681-689.    -   10. Hevroy E M, Boxaspen K, Oppedal F, Taranger G L, and Holm        J C. 2003. The effect of artificial light treatment and depth on        the infestation of the sea louse Lepeophtheirus salmonis on        Atlantic salmon (Salmo salar L.) culture. Aquaculture 220, 1-14.    -   11. Frenzl B, Stien L H, Cockerill D, Oppedal F, Richards R H,        Shinn A P, Bron J E, Migaud H. 2014. Manipulation of farmed        Atlantic salmon swimming behaviour through the adjustment of        lighting and feeding regimes as a tool for salmon lice control.        Aquaculture 424-425, 183-188.    -   12. Nilsen A et. al. Pilot Aqua Future. 2012. Sluttrapport 2013        05 28 ANI (in Norwegian)    -   13. Lien A M, Hoy E. 2011. Report: Skjort for skjerming mot lus        i laksemerd. SINTEF Fisheri og Havbruk A S. ISBN        978-82-14-05120-9 (in Norwegian)    -   14. Tveit K J. 2012. Nytt “luseskjort” stoppar lusa.(New        “sealice skirt” stops the sealice). Kyst.no 30.04.2102 (in        Norwegian).    -   15. Stien L H, Nilsson J, Hevroy E M, Oppedal F, Kristiansen T        S, Lien A M, and Folkedal O. 2012. Skirt around salmon sea cage        to reduce infestation of salmon lice resulted in low oxygen        levels. Aquaculture Engineering 51 (2012), 21-25.    -   16. Nylund A, Hovland T, Hodneland K., Nilsen F, and        Lovik P. 1994. Mechanisms for transmission of infectious salmon        anaemia (ISA). Diseases of Aquatic Organisms. Vol. 19:95-100.    -   17. Nylund S, Nylund A, Watanabe K, Arnesen C E,        Karlsbakk E. 2010. Paranucleospora theridion n. gen., n. sp.        (Microsporidia, Enterocytozoonidae) with a life cycle in the        Salmon louse (Lepeophtheirus salmonicidae) and Atlantic salmon        (Salmo salar). The Journal of Eukariotic Microbiology. Mar-Apr.        57(2): 95-114.    -   18. Jakob E, Barker D E, and Garver K A. 2011. Vector potential        of the salmon louse Lepeophtheirus salmonicidae in the        transmission of infectious hematopoietic necrosis virus (IHNV).        Disease of Aquatic Organisms (2011) 97(2), 155-65.    -   19. Torrisen O, Jones S, Asche F, Guttormsen A, Skilbreid O T,        Nilsen F, Horsberg T E and Jackson D. 2013. Salmon lice—impact        on wild salmonids and salmon aquaculture. Journal of Fish        Diseases 36(3), 171-94.    -   20. Krkosek M, Revie C W, Gargan P G, Skilbreid O T, Finstad B,        and Todd C D. 2013. Impact of parasites on salmon recruitment in        the Northeast Atlantic Ocean. Proc R Soc B. 280: 20122359.    -   21. Costello, M. J. 2009b. How sealice from salmon farms may        cause wild salmonids declines in    -   Europe and North-America and be threat to fishes elsewhere.        Proceedings of the Royal Society 276, 3385-3394.    -   22. Aldrin, M., Storvik, B., Kristoffersen, A. B., Jansen, P. A.        (2013). Space-time modelling of the spread of salmon lice        between and within Norwegian Salmon Farms. www.plosone.org.    -   23. Skiftesvik A B, Bjelland R M, Durif C M F, Johansen I S, and        Brownman H I. 2013. Delousing of Atlantic salmon (Salmo salar)        by cultured vs. wild ballan wrasse (Labrus bergylta).        Aquaculture 402-403 (2013) 113-118.    -   24. Costello, M. J. 2009a. The global economic cost of sealice        to the salmonide farming industry. Journal of Fish Diseases 32,        115-118.

25. Asche F, Bjorndal T. The economics of Salmon Aquaculture.Chichester: Wiley-Blackwell; 2011.

-   -   26. Ministry of Trade, Industry and Fisheries. Predictable and        environmentally sustainable growth in Norwegian salmon and trout        farming industry. White Paper to The Parliament 2015.        http://www.regieringen.no/no/aktuelt/barekraftig-og-forutsigbar-vekst-for-laks/id2401801/(Norwegian)    -   27. Norwegian Regulation regarding mandatory fallowing periods        per site. Chapter 4 § 40.        https://lovdata.no/dokument/SF/forskrift/2008-06-17-822#KAPITTEL        4    -   28. Norwegian Regulation regarding zone fallowing for the        prevention and combating of Salmon lice in Hardanger and        Sunnhordland. § 11.    -   29. Overview over sites in which Norwegian Food Safety Authority        has enacted reduction of production capacity due to        unsatisfactory levels of Salmon lice.        http://www.mattisynet.no/fisk_og_(—akvakultur/fiskehelse/)    -   30. Bleie H, Skrudland A. 2014. Tap av laksefisk i sjo. Food        Safety Authority, Norway. (Norwegian, English summary)    -   31. Nofima data—to come    -   32. Ytrestoyl T, Aas T S, Åsgård T. 2014. Resource utilisation        of Norwegian salmon farming in 2012 and 2013. Nofima report        36/2014. www.nofima.no.    -   33. Ytrestoyl T, Loes A K, Kvande I, Martinsen S, and Berge        G M. 2013. Utilisation of fish faeces in biogas production:        Technology and possibilities. ISBN: 987-82-8296-067-0.        www.nofima.no    -   34. Norwegian Directorate of Fisheries statistics of escapees.        (Norwegian)        http://www.fiskeridir.no/Akvakultur/Statistikk-akvakultur/Roemmingsstatistikk    -   35. Thorstad E B, Flemming I A, McGinnity P, Soto D, Wennevik V,        and Whoriskey F. 2008. Incidence and impacts of escaped farmed        atlantic salmon Salmo salar in nature. Norwegian Institute for        Nature Research. Special report 36, 110 pp.    -   36. Dempster T, Jensen O, Fredheim A, Uglem I, Thorstad E,        Somarakis S, and Sanchez-Jerez P. 2013. Escapes of fishes from        European sea-cage aquaculture: environmental consequences and        the need to better prevent escapes. PREVENT ESCAPE Project        compendium. ISBN 978-82-14-05565-8. www.preventescape.eu

The invention claimed is:
 1. A fish rearing tank, comprising: anegg-shaped shell with a generally vertical long axis and graduallynarrowing shape towards its tip volume portion; said shell forming agenerally rigid tank; said shell being closed; said shell having one ormore water inlets; said shell having one or more water outlets; saidegg-shaped tank for holding a water volume in its major lower volumeportion and enclosing air in its minor, upper tip volume portion; anaxial oriented central tube extending from the upper tip portion of theegg-shaped shell to the lower, wider end of said egg-shaped shell; and avertical axially running folding fish grid comprising a water-permeablecentral frame with running wheels for running on said central tube, saidfish grid having folding wings with guiding wheels at their outer ends,said folding wings arranged for folding in towards said central tube andfurther arranged for folding out with their outer ends arranged forfollowing the inner surface of said egg-shaped shell.
 2. The fishrearing tank of claim 1, further comprising a ring-shaped buoyancycollar mounted on said egg-shaped shell.
 3. The fish rearing tank ofclaim 2, said ring-shaped buoyancy collar arranged near said tipportion, for holding said egg-shaped shell in a semi-submerged positionwith said tip portion extending above the sea surface.
 4. The fishrearing tank of claim 2, said ring-shaped buoyancy collar arranged neara widest “equatorial” position of said egg-shaped shell, saidring-shaped buoyancy collar further having a ring-shaped water ballasttank for submerging said egg-shaped shell with its tip portion below thesea surface.
 5. The fish rearing tank of claim 1, further comprising afixed ballast in the broader, lower end of said egg-shaped shell.
 6. Thefish rearing tank of claim 1, further comprising: said at least onewater inlets arranged in the lower portion of the egg-shaped shell; andsaid water outlet near below an internal water surface level of theegg-shaped shell, so as for allowing bottom to top or“reverse”-circulation of water through the egg-shaped shell whilemaintaining said air volume in said tip.
 7. The fish rearing tank ofclaim 6, wherein said water inlet is horizontal and tangentiallydirected into the water within said egg-shaped shell.
 8. The fishrearing tank of claim 6, wherein said water inlets are arranged justabove said fixed ballast.
 9. The fish rearing tank of claim 6, furthercomprising a lower inlet pump arranged at the lower end of said centraltube.
 10. The fish rearing tank of claim 9, further comprising at leastone water inlet arranged through the side wall of said central tube towithin the water volume of said shell.
 11. The fish rearing tank ofclaim 1, further comprising a passage near the perimeter of the internalwater surface, to a circular holding tank arranged around said shell,said circular holding tank for holding sludge, non-eaten fodder, fishexcrements, and provided with a drain for excess water.
 12. The fishrearing tank of claim 1, wherein said folding fish grid is arranged forbeing stored in a folded-in position within the air above the internalwater surface level, within said upper tip portion, wherein said foldedfish grid is arranged for being lowered to a position below the internalwater surface in the egg-shaped shell, wherein said fish grid isarranged for being unfolded for the folding wings to engage with theinner surface of the egg-shaped shell, and wherein said unfolded fishgrid arranged for being elevated to force part of all of the fish abovesaid fish grid to move upwardly toward the upper tip portion.
 13. Thefish rearing tank of claim 1, further comprising ellipsoid grid bars, insaid fish grid arranged for being rotated between a closed positionimpenetrable for fish, to a partly or fully open position wherein fishbelow a given grating size may pass said fish grid.
 14. The fish rearingtank of claim 1, further comprising a vertical mooring line arrangedfrom extending from a hydraulic cylinder or winch within said axialoriented central tube near the upper tip portion and downwardly throughthe lower end of said central tube to an anchor below the egg-shapedshell.
 15. The fish rearing tank of claim 1, further comprising an airvalve arranged above the internal water level in the air volume withinsaid tip, so as for letting out air in order to reduce the floatabilityof the egg when going to submergence.
 16. The fish rearing tank of claim15, wherein said air valve is arranged at the upper allowable internalwater level within said otherwise air-filled tip.
 17. The fish rearingtank of claim 16, further comprising a ventilation fan in saidair-filled tip that also regulates adequate air intake.
 18. The fishrearing tank of claim 1, wherein feeding pipes are arranged from abovethe internal water surface, within the central tube and having an exitbelow water from the central tube, and wherein an air driven piston atthe top of the feeding pipes is arranged for moving downwardly after thepellet fodder has been fed into the pipe, to push fodder out of thelower opening to provide fish with a batch of fodder.
 19. The fishrearing tank of claim 1, wherein said shell is seamless.
 20. The fishrearing tank of claim 1, wherein said egg-shaped shell generally has adouble wall.
 21. The fish rearing tank of claim 1, wherein the volume ofsaid egg-shaped shell is between 4500 m3 and 22000 m3 or more.
 22. Thefish rearing tank of claim 1, wherein the diameter of the intake pipe is2250 mm.
 23. The fish rearing tank of claim 1, wherein the waterdischarge module is directed with an outlet direction along with thewater rotation generated by the inlet direction of the tangential waterinlets.
 24. A method of rearing fish, comprising the steps of: providinga fish rearing tank, comprising: an egg-shaped shell with a generallyvertical long axis and gradually narrowing shape towards its tip volumeportion; said shell forming a generally rigid tank; said shell beingclosed; said shell having one or more water inlets; said shell havingone or more water outlets; and said egg-shaped tank for holding a watervolume in its major lower volume portion and enclosing air in its minor,upper tip volume portion; placing a number of fish in said egg-shapedshell; circulating in fresh seawater through said water inlets arrangedin the lower portion of the egg-shaped shell; circulating out used waterthrough said water outlet near below an internal water surface level ofthe egg-shaped shell so as for conducting bottom to top or“reverse”-circulation of water through the egg-shaped shell whilemaintaining its air-filled volume in said tip; and for moving all orpart of the fish within the shell; providing a vertical axially running,folding fish grid comprising a water-permeable central grating framewith running wheels for running on an axial central tube, said fish gridhaving folding wings, preferably with guiding wheels at their outerends, said folding wings arranged for folding in towards said centraltube and further arranged for folding out with their outer ends arrangedfor following the inner surface of said egg-shaped shell; running saidfolded grating frame to the lower end of said egg-shaped shell;unfolding said grating frame for said folding wings to reside with theirouter ends near or at said inner surface of said egg-shaped shell;adjusting the grating so as for enabling sorting or moving a part or allof the contained fish population; and running said grating frameupwardly while said folding wings follow said inner surface of saidegg-shaped shell thereby sorting or moving said part of the containedfish.
 25. The method of claim 24, further comprising opening an airvalve to let out part of the air contained in said tip, and allowing thetip to submerge to a desired depth below the sea surface, whileconducting the circulation of water through the shell.
 26. The method ofclaim 24, further comprising controlling the water content in a ballasttank about said shell, and allowing the tip to submerge to a desireddepth below the sea surface, while conducting the circulation of waterthrough the shell.
 27. The method of claim 24, further comprisingtightening a mooring line, and allowing the tip to submerge to a desireddepth below the sea surface, while conducting the circulation of waterthrough the shell.
 28. The method of claim 24, further comprisingfolding in said folding wings and running said central grating frame toabove the water surface for internal storage while not in use forgrating.
 29. The method of claim 24, further comprising pumping in watertangentially through said water inlets near the lower end of said shellso as for generating a rotational and upward water movement through saidshell to water discharge modules near below the internal water surface.30. The method of claim 29, further comprising allowing said rotationaland upward water movement about said central axial tube.
 31. The methodof claim 30, further comprising, due to the rotational rising watermovement, allowing particles to concentrate at the internal watersurface towards the perimeter of the tank, and letting out said surfaceparticles to move out over a passage to said sludge holding tank. 32.The method of claim 24, further comprising loading feed into one or morefeeding pipes mounted inside the centre tube and extending between 3meters above water level and end approximately 5 and 10 meters above thebottom of the tank at which point they exit the tube into the tank,driving an air driven piston downwardly after the filling with desiredvolume of feed into the pipe, pushing the feed downwards and out of thelower opening of the pipe providing fish with batches of feed.